1. Field of the Invention
The present invention relates to a method of manufacturing an electroconductive film and the image-forming apparatus including the electroconductive film.
A conventional surface conduction electron-emitting device is shown in FIGS. 11A and 11B. FIG. 11A is a schematic plane view showing a conventional electron-emitting device, and FIG. 11B is a schematic cross-sectional view taken along a line 11B–11B in FIG. 11A.
Referring to FIGS. 11A and 11B, reference numeral 11 denotes an insulating substrate, 7 denotes an electron emission electroconductive film, 2 and 3 denote electrodes, and 8 denotes an electron-emitting portion.
FIG. 12 is a schematic structural view showing an example of an image display device as an image-forming apparatus using the electron-emitting device such as the surface conduction electron-emitting device shown in the above-mentioned FIGS. 11A and 11B.
In FIG. 12, reference numeral 81 denotes a substrate, 82 denotes an outer frame, and 86 denotes a face plate in which an image forming member 84 is disposed. The respective connecting portions of the outer frame 82, the substrate 81 and the face plate 86 are sealed with an adhesive such as a low melting point glass frit (not shown) to structure an envelope (air tight vessel) 88 for maintaining the interior of the image display device in a vacuum state.
A substrate 11 is fixed on the substrate 81. On the substrate 11 are arranged n×m electron-emitting devices 74 (n and m are positive integers of 2 or more and appropriately set in accordance with the number of target display pixels).
Also, the respective electron-emitting devices 74 are connected to wirings 4 and 6 formed of electroconductive films. The wirings in FIG. 12 are formed of m column-directional wirings 4 and n row-directional wirings 6 (also called “matrix wiring”). An insulating layer (not shown) is disposed on each cross portion of the row-directional wirings 6 and the column-directional wirings 4 to insulate the row-directional wirings 6 and the column-directional wirings 4 from each other.
In formation of the above image display device, it is necessary to form a large number of row-directional wirings 6 and column-directional wirings 4.
As a method of arranging and forming a large number of row-directional wirings 6 and column-directional wirings 4, a method of forming wirings formed of electroconductive films by using a printing technique which is relatively inexpensive, does not require a vacuum device or the like and can cope with a large area is disclosed in Japanese Patent Application Laid-open No. 8-34110 and the like.
In order to make the image-forming apparatus such as the above image display device higher in its precision, it is necessary to form the wirings formed of the electroconductive film that supplies an electricity to the respective electron-emitting devices to drive the respective electron-emitting devices with higher precision.
Under the above circumstances, in formation of the above wirings, a method using photosensitive paste has been proposed.
Also, in a case of fabricating a large-area image-forming apparatus having a diagonal of several tens cm, it is necessary to make the wirings used in the interior of the image-forming apparatus lower in resistance. To achieve this, it is important to make the film thickness of the wirings thick.
However, in a case of using the photosensitive paste for the purpose of forming the thick wirings with high precision, there arise the following problems.
In general, a process of fabricating the wirings in the case of using the photosensitive paste is conducted in a stated order of forming of the photosensitive paste film, (drying), exposing, developing and burning.
However, in the case of fabricating the wirings by forming a thick photosensitive paste film at once and then sequentially implementing (drying), exposing, developing and baking processes for the purpose of forming the thick film, there arise the following problems.
That is, in FIGS. 13A to 13D where reference numeral 11 denotes a substrate, 12 denotes a photosensitive paste, 13 denotes a mask, 14 denotes an exposed light, 15 denotes a latent image, 19 denotes a develop pattern as a developing image and 21 denotes a completed wiring pattern, FIG. 13A shows a film forming process, FIG. 13B is an exposure process, FIG. 13C is a developing process and FIG. 13D is a baking process. In the case of fabricating the wirings in that order, a curl of an edge portion of the wiring pattern 21 that has been baked such as warping (hereinafter, referred to as “edge curl”) increases, and in further laminating an insulating layer on the wiring pattern in a succeeding process, spaces defined on both sides of the wiring pattern 21 under the edge curl portions are insufficiently filled with an insulating material, thereby coming to a state where spaces remain there.
It is presumed that this is caused by a reduction of volume resulting from evaporating a solvent or the like in the baking process of FIG. 13D, or the short of the amount of exposure at the time of exposing a light because of the thick photosensitive paste.
On the other hand, if the amount of exposure is increased to eliminate the short of the amount of exposure, a so-called over exposure is exhibited, resulting in cases where the sharpness of the edge portion of the wiring pattern 21 becomes low, or patterning is made with a width wider than a desired width.
Also, in forming a matrix wiring (row-directional wirings and column-directional wirings) used in an image display device shown in FIG. 12 among the wirings formed of the electroconductive film, in order to insulate the row-directional wirings and the column-directional wirings from each other, it is necessary that after a lower-layer wiring positioning at a lower side has been formed, an insulating layer is formed, and therefore an upper-layer wiring is laminated thereon.
For that structure, in the case of using a wiring with the above curled edge portions as the lower-layer wiring at the lower side, an insulating layer is formed on the lower-layer wiring with the curled edges.
In this situation, in forming the insulating layer through a printing method, the spaces on both sides of the lower-layer wiring at the lower-side of the curled edge portion cause bubbles to be produced in the insulating layer in the baking process required for the printing method.
As a result, the bubbles within the insulating layer deteriorate the insulating property between the row-directional wirings and the column-directional wirings, and in the worst case, there may occur such a problem that the row-directional wirings and the column-directional wirings are short-circuited.
Also, in the above-mentioned image-forming apparatus, a high voltage of several kV to several tens kV is applied to a metal back arranged in the face plate. For that reason, when a wiring (electroconductive film) with the above-mentioned curled edges exists on a facing rear plate, the possibility that a discharge phenomenon starting from the curled edge portions occurs becomes high.
The curled edges in question are remarkably observed when the film thickness of the photosensitive paste that has been baked exceeds 5 μm, and the amount of curled edge becomes larger as the film thickness becomes thick.
For example, in the case where the thickness of a portion A that has been baked in FIG. 13D is 10 μm, the curled edge which is the film thickness of a portion B in FIG. 13D becomes 18 to 21 μm.
The film thickness of the portion A exhibits a height of a portion except for the curled edge portion on the wiring pattern 21 end portion that has been baked from the substrate surface. The film thickness of the portion B exhibits a height of the curled edge portion of the wiring pattern 21 end portion.
For that reason, the curled amount of edge (B/A) is about twice. In the present specification, the curled amount of edge is directed to a ratio of B to A in FIG. 13D, and in this case, that the curled amount of edge is about twice means B/A=(18/10) to (12/10) ≅2.
If the curled amount of edge is thus about twice, in the case of forming the above-mentioned matrix wirings, the formation of the insulating layer which will be laminated in a following process is adversely affected due to only the height of the curled edge portion.
There is a case in which the curled amount of edge is equal to the thickness of substantially one layer of the insulating layer although depending on the thickness of the insulating layer, and in this case, the thickness of the substantially one insulating layer is canceled by the curled amount of edge.
For that reason, if a desired insulating performance is going to be obtained, it becomes necessary to form an excessively thicker insulating layer taking the curled amount of edge into consideration. In addition, as a result of forming the thicker insulating layer in formation of the upper-layer wiring at the upper side after the insulating layer has been formed, an excessive step is formed, resulting in the disconnection of the upper-layer wiring at the upper side.
Also, on terminals (lead-out) of the wirings in the image-forming apparatus, in the case where there are the curled edge portion, if flexible mounting is going to be conducted, the curled edge portion may be destroyed or a contact failure may occur.